genirq/timings: Add selftest for circular array

Due to the complexity of the code and the difficulty to debug it, add some
selftests to the framework in order to spot issues or regression at boot
time when the runtime testing is enabled for this subsystem.

This tests the circular buffer at the limits and validates:
 - the encoding / decoding of the values
 - the macro to browse the irq timings circular buffer
 - the function to push data in the circular buffer
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: andriy.shevchenko@linux.intel.com
Link: https://lkml.kernel.org/r/20190527205521.12091-7-daniel.lezcano@linaro.org

kernel/irq/Makefile

@@ -2,6 +2,9 @@
 
 obj-y := irqdesc.o handle.o manage.o spurious.o resend.o chip.o dummychip.o devres.o
 obj-$(CONFIG_IRQ_TIMINGS) += timings.o
+ifeq ($(CONFIG_TEST_IRQ_TIMINGS),y)
+	CFLAGS_timings.o += -DDEBUG
+endif
 obj-$(CONFIG_GENERIC_IRQ_CHIP) += generic-chip.o
 obj-$(CONFIG_GENERIC_IRQ_PROBE) += autoprobe.o
 obj-$(CONFIG_IRQ_DOMAIN) += irqdomain.o

kernel/irq/timings.c

 // SPDX-License-Identifier: GPL-2.0
 // Copyright (C) 2016, Linaro Ltd - Daniel Lezcano <daniel.lezcano@linaro.org>
+#define pr_fmt(fmt) "irq_timings: " fmt
 
 #include <linux/kernel.h>
 #include <linux/percpu.h>
 #include <linux/slab.h>
 #include <linux/static_key.h>
+#include <linux/init.h>
 #include <linux/interrupt.h>
 #include <linux/idr.h>
 #include <linux/irq.h>
@@ -625,3 +627,120 @@ int irq_timings_alloc(int irq)
 
 	return 0;
 }
+
+#ifdef CONFIG_TEST_IRQ_TIMINGS
+static int __init irq_timings_test_irqts(struct irq_timings *irqts,
+					 unsigned count)
+{
+	int start = count >= IRQ_TIMINGS_SIZE ? count - IRQ_TIMINGS_SIZE : 0;
+	int i, irq, oirq = 0xBEEF;
+	u64 ots = 0xDEAD, ts;
+
+	/*
+	 * Fill the circular buffer by using the dedicated function.
+	 */
+	for (i = 0; i < count; i++) {
+		pr_debug("%d: index=%d, ts=%llX irq=%X\n",
+			 i, i & IRQ_TIMINGS_MASK, ots + i, oirq + i);
+
+		irq_timings_push(ots + i, oirq + i);
+	}
+
+	/*
+	 * Compute the first elements values after the index wrapped
+	 * up or not.
+	 */
+	ots += start;
+	oirq += start;
+
+	/*
+	 * Test the circular buffer count is correct.
+	 */
+	pr_debug("---> Checking timings array count (%d) is right\n", count);
+	if (WARN_ON(irqts->count != count))
+		return -EINVAL;
+
+	/*
+	 * Test the macro allowing to browse all the irqts.
+	 */
+	pr_debug("---> Checking the for_each_irqts() macro\n");
+	for_each_irqts(i, irqts) {
+
+		irq = irq_timing_decode(irqts->values[i], &ts);
+
+		pr_debug("index=%d, ts=%llX / %llX, irq=%X / %X\n",
+			 i, ts, ots, irq, oirq);
+
+		if (WARN_ON(ts != ots || irq != oirq))
+			return -EINVAL;
+
+		ots++; oirq++;
+	}
+
+	/*
+	 * The circular buffer should have be flushed when browsed
+	 * with for_each_irqts
+	 */
+	pr_debug("---> Checking timings array is empty after browsing it\n");
+	if (WARN_ON(irqts->count))
+		return -EINVAL;
+
+	return 0;
+}
+
+static int __init irq_timings_irqts_selftest(void)
+{
+	struct irq_timings *irqts = this_cpu_ptr(&irq_timings);
+	int i, ret;
+
+	/*
+	 * Test the circular buffer with different number of
+	 * elements. The purpose is to test at the limits (empty, half
+	 * full, full, wrapped with the cursor at the boundaries,
+	 * wrapped several times, etc ...
+	 */
+	int count[] = { 0,
+			IRQ_TIMINGS_SIZE >> 1,
+			IRQ_TIMINGS_SIZE,
+			IRQ_TIMINGS_SIZE + (IRQ_TIMINGS_SIZE >> 1),
+			2 * IRQ_TIMINGS_SIZE,
+			(2 * IRQ_TIMINGS_SIZE) + 3,
+	};
+
+	for (i = 0; i < ARRAY_SIZE(count); i++) {
+
+		pr_info("---> Checking the timings with %d/%d values\n",
+			count[i], IRQ_TIMINGS_SIZE);
+
+		ret = irq_timings_test_irqts(irqts, count[i]);
+		if (ret)
+			break;
+	}
+
+	return ret;
+}
+
+static int __init irq_timings_selftest(void)
+{
+	int ret;
+
+	pr_info("------------------- selftest start -----------------\n");
+
+	/*
+	 * At this point, we don't except any subsystem to use the irq
+	 * timings but us, so it should not be enabled.
+	 */
+	if (static_branch_unlikely(&irq_timing_enabled)) {
+		pr_warn("irq timings already initialized, skipping selftest\n");
+		return 0;
+	}
+
+	ret = irq_timings_irqts_selftest();
+
+	pr_info("---------- selftest end with %s -----------\n",
+		ret ? "failure" : "success");
+
+	return ret;
+}
+early_initcall(irq_timings_selftest);
+#endif

lib/Kconfig.debug

@@ -1858,6 +1858,14 @@ config TEST_PARMAN
 
 	  If unsure, say N.
 
+config TEST_IRQ_TIMINGS
+	bool "IRQ timings selftest"
+	depends on IRQ_TIMINGS
+	help
+	  Enable this option to test the irq timings code on boot.
+
+	  If unsure, say N.
+
 config TEST_LKM
 	tristate "Test module loading with 'hello world' module"
 	depends on m